Internal electrical contact for enclosed mems devices

ABSTRACT

A method of fabricating electrical connections in an integrated MEMS device is disclosed. The method comprises forming a MEMS wafer. Forming a MEMS wafer includes forming one cavity in a first semiconductor layer, bonding the first semiconductor layer to a second semiconductor layer with a dielectric layer disposed between the first semiconductor layer and the second semiconductor layer, and etching at least one via through the second semiconductor layer and the dielectric layer and depositing a conductive material on the second semiconductor layer and filling the at least one via. Forming a MEMS wafer also includes patterning and etching the conductive material to form one standoff and depositing a germanium layer on the conductive material, patterning and etching the germanium layer, and patterning and etching the second semiconductor layer to define one MEMS structure. The method also includes bonding the MEMS wafer to a base substrate.

CROSS-REFERENCE TO RELATED APPLICATION

Under 35 U.S.C. 120, this application is a Continuation Application andclaims priority to U.S. application Ser. No. 14/456,973, filed Aug. 11,2014, entitled “INTERNAL ELECTRICAL CONTACT FOR ENCLOSED MEMS DEVICES,”which is a Continuation Application and claims priority to U.S.application Ser. No. 14/033,366, filed Sep. 20, 2013, entitled “INTERNALELECTRICAL CONTACT FOR ENCLOSED MEMS DEVICES,” which is a DivisionalApplication and claims priority to U.S. patent application Ser. No.13/754,462, filed on Jan. 30, 2013, entitled “INTERNAL ELECTRICALCONTACT FOR ENCLOSED MEMS DEVICES,” all of which are incorporated hereinby reference.

FIELD OF THE INVENTION

The present invention relates generally to MEMS devices and morespecifically to providing electric contact of the enclosure of the MEMSdevices.

BACKGROUND

MEMS devices are utilized in a variety of environments. In such devicesa handle layer is normally required to be electrically grounded toprovide an electric shield for low noise performance. The electricalconnection to the handle layer is provided by a wire bond. However, thewire bond requires vertical space and increases overall thickness of theMEMS device when packaged. Accordingly, what is desired is a MEMS deviceand method where the wire bond is not necessary.

The MEMS device and method for providing electrical connection to thehandle layer should be simple, easily implemented and adaptable toexisting environments. The present invention addresses such a need.

SUMMARY

A method of fabricating electrical connections in an integrated MEMSdevice is disclosed. The method comprises forming a MEMS wafer. Forminga MEMS wafer includes forming one cavity in a first semiconductor layer,bonding the first semiconductor layer to a second semiconductor layerwith a dielectric layer disposed between the first semiconductor layerand the second semiconductor layer, and etching at least one via throughthe second semiconductor layer and the dielectric layer and depositing aconductive material on the second semiconductor layer and filling the atleast one via. Forming a MEMS wafer also includes patterning and etchingthe conductive material to form one standoff and depositing a germaniumlayer on the conductive material, patterning and etching the germaniumlayer, and patterning and etching the second semiconductor layer todefine one MEMS structure. The method also includes bonding the MEMSwafer to a base substrate.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a diagram which illustrates a cross-section of the bondedMEMS-base substrate device with an internal direct electric coupling inaccordance with a first embodiment.

FIGS. 2A-2E are diagrams which illustrate a series of cross-sectionsillustrating processing steps to build the electric coupling from handlelayer to MEMS device layer ready to bond to a base substrate for thedevice of FIG. 1.

FIG. 3 is a diagram which illustrates a cross-section of the bondedMEMS-base substrate device with an internal direct electric coupling inaccordance with a second embodiment.

FIG. 4 is a diagram which illustrates a cross-section of the bondedMEMS-base substrate device with an internal direct electric coupling inaccordance with a third embodiment.

FIGS. 5A-5G are diagrams which illustrate a series of cross-sectionsillustrating processing steps to build the electric coupling from handlelayer to MEMS device layer ready to bond to a base substrate for thedevice of FIG. 4.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS

The present invention relates generally to MEMS devices and morespecifically to electric coupling for enclosed CMOS-MEMS devices. Thefollowing description is presented to enable one of ordinary skill inthe art to make and use the invention and is provided in the context ofa patent application and its requirements. Various modifications to thepreferred embodiment and the generic principles and features describedherein will be readily apparent to those skilled in the art. Thus, thepresent invention is not intended to be limited to the embodiment shownbut is to be accorded the widest scope consistent with the principlesand features described herein.

In the described embodiments Micro-Electro-Mechanical Systems (MEMS)refers to a class of structures or devices fabricated usingsemiconductor-like processes and exhibiting mechanical characteristicssuch as the ability to move or deform. MEMS often, but not always,interact with electrical signals. MEMS devices include but are notlimited to gyroscopes, accelerometers, magnetometers, pressure sensors,and radio-frequency components. Silicon wafers containing MEMSstructures are referred to as MEMS wafers.

In the described embodiments, MEMS device may refer to a semiconductordevice implemented as a micro-electro-mechanical system. MEMS structuremay refer to any feature that may be part of a larger MEMS device. Anengineered silicon-on-insulator (ESOI) wafer may refer to a SOI waferwith cavities beneath the silicon device layer or substrate. Handlewafer typically refers to a thicker substrate used as a carrier for thethinner silicon device substrate in a silicon-on-insulator wafer. Handlesubstrate and handle wafer can be interchanged.

In the described embodiments, a cavity may refer to an opening orrecession in a substrate wafer and enclosure may refer to a fullyenclosed space.

To describe the features of the invention in more detail, apparatus andfabrication methods to achieve a direct electric coupling of handlelayer, device layer and base substrate of a MEMS device without a metalwire-bond are disclosed.

FIG. 1 is a diagram which illustrates a cross-section of the bondedMEMS-base substrate device with an internal direct electric coupling inaccordance with a first embodiment. An engineered silicon-on-insulator(ESOI) substrate 120 includes a handle layer 101 with cavities 112 and adevice layer 104, fusion bonded together with a thin dielectric film 103(such as silicon oxide) in between the device layer 104 and handle layer101. An electrical connection between the handle layer 101 and thedevice layer 104 may be achieved by etching one or more vias 106 throughthe device layer 104 and the thin dielectric layer 103 into the handlelayer 101 and by filling the vias 106 with a conductive material 114,such as polysilicon, tungsten, titanium, titanium nitride, aluminum, orgermanium. The MEMS substrate is considered complete after a germanium(Ge) 109 and standoffs 105 comprising conductive material 114 are formedand MEMS actuator structures are patterned and etched in device layer104. Alternately, the standoff can be formed from both the conductivematerial 114 and a portion of the device layer 104 by partially etchinginto the device layer during standoff formation. In other embodimentsthe base substrate can comprise CMOS circuitry.

The MEMS to a base substrate integration may be provided by eutecticbonding of germanium 109 of the MEMS substrate with aluminum 107 of abase substrate 102, where the AlGe bond provides the direct electricalcoupling between MEMS substrate (handle 101 and device 104) and basesubstrate 102. In addition, AlGe bond provides hermetic vacuum seal ofthe MEMS device.

FIGS. 2A-2E are diagrams which illustrate a series of cross-sectionsillustrating processing steps to build the electric coupling from handlelayer 101 to MEMS device layer 104 ready to bond to a base substrate 102shown in FIG. 1.

FIG. 2A is a diagram which illustrates the cross-section of an ESOI(engineered SOI) substrate with device layer 104 fusion-bonded to ahandle silicon layer 101 with cavities 112. In an embodiment, as shownin FIG. 2B, vias 106 are patterned on device layer 104 of ESOI substrateand etched through device layer 104, through thin dielectric layer 103,and into handle layer 101. In another embodiment, vias 106 are patternedon device layer 104 of ESOI substrate and etched through device layer104 and through thin dielectric layer 103 to expose a portion of thesurface of handle layer 101. A conformal deposition of a conductivematerial 105 is then provided, as shown in FIG. 2C, to fill via 106 toestablish electrical coupling between device layer 104 and handle layer101. A germanium layer 109 is then deposited onto the conductivematerial 105. The next step shown in FIG. 2D is to pattern and etchconductive material 105 and germanium layer 109 to form standoffs 121from the conductive material 105, followed by MEMS device layer 104pattern and etch, as shown in FIG. 2E to complete the MEMS substrateprocessing, ready to bond to a base substrate. Alternately, the standoff121 can be formed from both the conductive material 105 and a portion ofthe device layer 104 by partially etching into the device layer duringstandoff formation.

FIG. 3 is a diagram which illustrates a cross-section of the bondedMEMS-base substrate device with an internal direct electric coupling inaccordance with a second embodiment. In this embodiment, the electriccoupling path is formed from handle layer 201 to MEMS device layer 204,across dielectric film 203, and eventually to base substrate Al pad 207after MEMS to base substrate AlGe eutectic bonding.

An ESOI substrate 220 is comprised of a handle layer 201 with cavities212 and a device layer 204, fusion bonded together with a thindielectric layer 203 (such as silicon oxide) in between the device layer204 and handle layer 201. The ESOI substrate is completed after devicelayer thinning. An electrical connection between handle layer 201 anddevice layer 204 can be achieved by etching at least one via 206 at anylocations through device layer 204 and thin dielectric layer 203 into orexposing the surface of handle layer 201 and filling the via 206 byconductive materials, such as polysilicon, tungsten, titanium, titaniumnitride, aluminum or germanium. In this embodiment, the remainingconductive materials on device layer 204 could be removed by thinning,polishing or etching-back to expose device layer for standoff formation205. Steps of germanium deposition, standoff pattern, germanium etch,device layer 204 pattern, and etch, will be processed to complete theMEMS substrate.

The MEMS-base substrate integration is achieved by eutectic bonding ofMEMS substrate with germanium pads 209 to base substrate with aluminumpads 207, where the AlGe bonding provides direct electrical couplingbetween MEMS substrate (handle 201 and device 204) and base substrate202. In an embodiment, the standoff 205 forms a ring around the MEMSstructure, the AlGe bond provides a hermetic seal for the MEMSstructure. Via 206 can be positioned within or outside the seal ringformed by the standoff 205.

FIG. 4 is a diagram illustrating a third embodiment of the electriccoupling between handle layer 301, MEMS device layer 304, and basesubstrate 302 using polysilicon for the device layer 304 and AlGeeutectic bonding. The process flow and fabrication method of MEMSsubstrate using a surface micro-machining process technique areillustrated in FIGS. 5A-5F. FIGS. 5A-5F are diagrams which illustrate aseries of cross-sections illustrating processing steps to build theelectric coupling from handle layer 301 to device layer 306 ready tobond to a base substrate 302 for the device of FIG. 4. Starting fromFIG. 5A, a thin dielectric layer 303 (typically silicon oxide) isdeposited on a handle layer 301. Thereafter the layer 303 is patternedand etched to form vias 312. A silicon layer 306 (FIG. 5B) is depositedonto the handle layer 301 followed by thinning and planarization, (forexample grinding or chemical mechanical polishing) to desired devicelayer thickness. FIG. 5C illustrates an embodiment with a second thickersilicon device layer. In this embodiment, an additional silicon wafer311 can be bonded to the thin polysilicon 312 and thinned down todesired device thickness. The bonding of the additional silicon wafer311 overcomes thickness limitations from conventional depositiontechniques.

A Ge layer 309 is then deposited, as shown in FIG. 5D. FIG. 5E is adiagram which illustrates standoff 305 formation by patterning andetching into device layer 306. FIG. 5F is a diagram which illustratespatterning and etching silicon layer 306 to form MEMS structure 304. Thepatterning and etching step is followed by etching the silicon oxide torelease the device layer 304 as shown in FIG. 5G. The MEMS substrate isnow ready to be integrated with a base substrate.

As shown in FIG. 4, the MEMS-base substrate integration is achieved byeutectic bonding of MEMS substrate with germanium pads 309 to basesubstrate with aluminum pads 307, where the AlGe bonding provides directelectrical coupling between MEMS substrate (handle 301 and device 305)and base substrate 302. In addition, AlGe bonding provides hermeticvacuum seal of the MEMS device.

Although the present invention has been described in accordance with theembodiments shown, one of ordinary skill in the art will readilyrecognize that there could be variations to the embodiments and thosevariations would be within the spirit and scope of the presentinvention. Accordingly, many modifications may be made by one ofordinary skill in the art without departing from the spirit and scope ofthe appended claims.

1.-9. (canceled)
 10. A MEMS device comprising: a MEMS substrate, theMEMS substrate includes a first semiconductor layer, a secondsemiconductor layer and a dielectric layer in between, the firstsemiconductor layer has a first and second surfaces, wherein the firstsurface is in contact with the dielectric layer; wherein MEMS structuresare formed from the second semiconductor layer and includes a pluralityof first conductive pads; a base substrate which includes a plurality ofsecond conductive pads thereon; wherein the second conductive pads areconnected to the first conductive pads; and a conductive connectorformed through only the dielectric layer, the second semiconductor layerand the first surface of the first semiconductor layer to provideelectrical coupling between the first semiconductor layer and the secondsemiconductor layer, whereby the base substrate is electricallyconnected to the second semiconductor layer and the first semiconductorlayer.
 11. The MEMS device of claim 10, wherein the plurality of firstconductive pads comprise germanium.
 12. The MEMS device of claim 10,wherein the plurality of second conductive pads comprise aluminum. 13.The MEMS device of claim 10, wherein the MEMS substrate includes one ormore etched vias filled by conductive material to form the conductiveconnector.
 14. The MEMS device of claim 10 further comprising a sealring, the seal ring comprising a continuous ring to form an enclosuresurrounding the MEMS structures and formed by a connection of one of thefirst conductive pads and one of the second conductive pads.
 15. TheMEMS device of claim 14, wherein the first conductive pad iselectrically connected to the first semiconductor layer.
 16. The MEMSdevice of claim 14, wherein the conductive connector is positioned inthe enclosure of the seal ring, or wherein the conductive connector ispositioned outside the enclosure of the seal ring.
 17. The MEMS deviceof claim 14, wherein the conductive connector is positioned within theseal ring.
 18. The MEMS device of claim 10, wherein the connectionbetween the first conductive pad and second conductive pad is a eutecticbond.
 19. The MEMS device of claim 10, wherein the MEMS structures areelectrically isolated from the first semiconductor layer.
 20. The MEMSdevice of claim 13, wherein the conductive material filling the one ormore vias comprises any of polysilicon, germanium, and tungsten, orwherein the conductive material filling the one or more vias comprisesany of aluminum, titanium, and titanium nitride.
 21. The MEMS device ofclaim 14, wherein the seal ring provides a hermetic seal.
 22. The MEMSdevice of claim 10, wherein surface of the first semiconductor layerfacing the second semiconductor layer includes cavities therein.
 23. TheMEMS device of claim 10, wherein the first semiconductor layer and thesecond semiconductor layer comprise any of single crystal siliconmaterials or polysilicon materials.